How do you make objects appear in a blender scene at specific times?
While you can animate the visibility of an object, I think you are more interested in adjusting the timing of the animation. Using the dopesheet you can select the keyframes of your animation and move them along to start at frame 245.

Similar tot he 3dview you can use A to select all keyframes and G to move them. After grabbing the keyframes you can also type in the number of frames you want to move them.



You may also be able to render two separate animations and join them together in the VSE